Best practices for temperature control during fermentation (STC-1000)?

[thehopbandit]

I built a STC-1000 temperature controller box to use with my ~5 cu. ft. chest freezer and have a couple questions as to the best practices to use with it.

1. Where is the best place to place the temp probe (see poll)? Right now I have it suspended in the air. I have heard that some people insulate it against the side of the carboy, but I feel like if you do that, the thermal mass that is the wort will take much longer to cool down or heat than the surrounding air. By the time the temp of the wort hits the desired temp, the surrounding air will be far, far colder and continue to cool it. Even with a heater to kick in, it seems like there is a big lag between the two. How do you manage this?

2. What about the overshoot of the temperature? With my setup, I have noticed about a 1.5-2°C overshoot. For instance, if F1 (the desired temp) was set at 18.3°C, the compressor will kick on, stop at 18.3°C but the temp will continue to creep down.

3. Fermentation will cause the beer to be a couple degrees higher than ambient temperature. What is the best practice here?

4. What are your general practices in managing your fermentation temperature? Settings of your controller? Processes? Do you keep a constant temp the entire fermentation, or do you start low and finish high? What are your tips?

Thanks for the help!

 

[Brews]

I insulate it against the side but now you've got me thinking. I would guess that you are correct in stating that the thermal mass would take much longer to cool or heat. But on that same note, once it does hit the desired temp. it should stay at that temp. much longer. I was also told that it helps keep the ferm. chamber from cycling too often. I have one in there right now and before I dry hop it, I'll check the temp to see the actual vs. the controller.

 

[divechief]

I'm a newbie (batch 7 just finished one week in primary) tried different things. first I tried insulating it against the fermenter. temperature swings were huge. latest batch (and I think my future procedure) I insulated it against the fermenter, and brought it down a couple degrees at a time until it hit my target temperature.

 

[betarhoalphadelta]

Insulate it against the fermenter. Yes, the internal air temp will swing wildly. But the fermenter temp will not. And it's the fermenter temp that is most important.

 

[SixStrings]

Since fermentation produces heat, I think it makes more sense to monitor the temperature of the beer itself. According to the probe, the air in your freezer may be sitting at it's ideal temp, say 65F, meanwhile the heat from fermentation is pushing your beer towards the 70s. Like you said, the thermal mass of the beer is much greater than the surrounding air, so to me it makes sense that it will be more resistant to temperature swings, even if the temps dip below what you've set on the controller.

Regarding 4: I'm not familiar with the STC-1000, but my with my Johnson controller I use a differential of 2 degrees and have it set to "cut-in" mode. It turns on the compressor once the temperature is equal to the setpoint, and shuts it off when it reaches the differential. It ensures that FV will never go over a certain temperature during fermentation, which I think is important if you're looking for a specific yeast flavor profile in your beers.

 

[BigFloyd]

I'm afraid that you're over-thinking this.

Measure the beer temp (on the side of the fermenter and insulated). The air temp doesn't matter except that it helps you regulate the beer temp. The beer temp takes much longer to change because the thermal mass of the air is very small vs. that of the beer. If you measure the air temp, you will see lots of fluctuation and you will not be able to accurately control your actual fermentation temp.

I'm well familiar with the STC-1000. I currently use three of them.

 

[thehopbandit]

Thanks for all of the replies. Very good points.

I think I'll try insulating it against the fermenter next time and see how it works. I just can't help but thinking about temperature swings, though. Since it will take a very long time to cool down the wort, the chest freezer's ambient will get down and be running around 0F (17.8C) for a long while until the wort, itself, comes down to the desired temperature. After the compressor shuts off, the inside of the chest will be pretty dang cold for a good while after shut off since it was all the way down at around 0F. In my mind I see this dragging down the temp of the fermenter even further as the ambient equalizes.

Obviously, this method works for a ton of people so I'm just going to have to test it out and see. I just can't help but think that large ambient overshoot will cause a further drop after the wort hits the desired temp and it shuts off. I'll have to try it!

 

[Rbeckett]

I drilled an extra hole in my lid and inserted a grommet and slide in a thermowell. The Thermowell has a K-type thermocouple and conductive grease. So what ever the STC is showing is the actual temp of the top 4 or 5 inches of wort in my brew pail. I usually set the temp to the lowest temp of the acceptable range to start out for the first couple of days, then I allow it to rise to the midpoint temp naturally and leave it there for the remaining two or three weeks. I don't open or peek at the brew till it is in the pail at least three weeks. If I am at or very close to my FG projection, I go ahead and bottle immediately. Back in the keezer at mid point temp with the probe buried in the middle of a stack of bottles for at least another two weeks. Been working extremely well for me so far.

Wheelchair Bob

 

[bobmcstuff]

I sterilise it and run it directly into the wort...

For a target temp of 18c it tends to go between 17.9c and 18.5c (when the cooler kicks back in) at high krausen, after that it tends to get down to around 17.6-17.7c (obviously due to lag in the system).

 

[Ryush806]

I use a nice stainless thermowell with a bung that has a hole for it and for the airlock. That way the probe sits dead center in the beer. The outer edges of the beer are about two degrees colder than the internal temp as evidenced by my stick on thermometer so I figure on average the beer may be one degree off set point.

 

[Wynne-R]

It seems to me you should put the insulation UNDER the probe. Not a lot, maybe a few layers of tape. This would give you shorter compressor cycles but it would still be responsive to the fermentation heat.

Somewhere between air and thermowell should be the sweet spot. Or maybe you could use the freezer thermostat to limit how cold it will get.

My fermentor is in a water tub and I control the temperature with an immersion chiller, an ice bucket and a pump. When I had the probe near the bottom of the tub the pump would run for about twenty minutes and be off for about forty. I moved the probe to be between the coils sticking out into the water and it runs 15-20 seconds every few minutes.

Temperature regulation on the water went from about ± .3C to unmeasurable, less than .1C variance. That’s with the differential set to .3C, but there’s always going to be overshoot.

My setup is unusual, but my point is that with creative placement of the probe you should be able to set your duty cycle where you want it. It’s not just air or beer, there’s a whole lot of in-between. It works for me in water, I don’t see why it wouldn’t work in air. Somebody try it and let me know.

 

[grathan]

Did the OP lower the setting for threshold? I know the default was higher than the minimum of 0.3

I 2nd the suggestion for stainless thermowell. Also wrapping the carboy in fermwrap and plugging into the hotside of the STC1000. Never overshoot again..

 

[aubiecat]

Hanging the sensor in the air only tell you temperature of the air not the wort in the carboy. Logical thinking will tell you that the temperature inside the carboy will always be much higher than the air in the fermenting unit.

A thermowell goes to the other side of the extreme. By the time the set temperature reaches the wort in the center of the carboy(where the sensor is) the temperature inside the ferm unit is probably freezing. Now the wort on the outside of the carboy is being subjected to extremely low temps and will cause a backlash once the set temp reaches the middle again.

Some people put the sensor in an old yeast vile with some type of liquid in it. That only tells what the temp is of the liquid in a small vile is. Meanwhile the temp in the carboy is always much higher than the liquid vile.

With a single senor temperature controller, taping or strapping the sensor to the side of the carboy with some insulation is the way to go.
In my experience that is the most consistent way to monitor the temp in fermenting wort.

 

[thehopbandit]

Did the OP lower the setting for threshold? I know the default was higher than the minimum of 0.3

I 2nd the suggestion for stainless thermowell. Also wrapping the carboy in fermwrap and plugging into the hotside of the STC1000. Never overshoot again..

Yep, I did mess around with the threshold. I have tried different settings from 1-2C. I'll probably need to do some more testing for my specific setup to really dial it in. I'll probably try the insulation method next time. Once the wort hits the desired temp, what variance threshold is good for the insulation method?

 

[grathan]

0.3 is the best it can do. My freezer kicks on every other hour so I wish it could go even lower.

 

[seigex]

http://morebeer.com/products/hood-thermowell-3-5-6-65-gallon-smooth-neck-carboys-15.html

or

http://morebeer.com/products/stopper-thermowell.html?site_id=5

 

[BigFloyd]

Yep, I did mess around with the threshold. I have tries different settings from 1-2C. I'll probably need to do some more testing for my specific setup to really dial it in. I'll probably try the insulation method next time. Once the wort hits the desired temp, what variance threshold is good for the insulation method?

In my fermenter chamber, I have my tolerance set to 0.7*C.

One thing that will help at the start of fermentation is to pitch your yeast at a degree or two LOWER than your target starting fermentation temp and let it come up slowly on its own to the desired temp. This will also help avoid off-flavors. If you put a bucket/carboy full of wort in there that's 8-10*F higher than the starting ferment temp, the fridge/freezer will have to cool way down in an effort to get that large amount of liquid down to the set temp.